Rheostat



March 22, 1938. N, c. SCHELLENGER 2,111,810

RHEOSTAT Original Filed May 26, 1933 4 Sheets-Sheet 1 inventor(IttomegS, v

March 22, 1938.

N. C. SCI-EELLENGER RHEOS TAT Original Filed May 26, 1935 4 Sheets-Sheet2 March 1938. IN. c. SCHELLENGER 2,111,810

RHEOSTAT Original Filed May 26, 1933 4 Sheets-Sheet 3 Nell/$072.asmezzmfiw.

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N. c. SCHELLENGER RHEOSTAT March 22, 1938.

Original Filed May 26, 1933 4 Sheets-Sheet 4 [Yea/tan 6, SeizeZig22WWWW, W f (Ittornegfi,

Patented Mar. 22,1938

UNITED STATES OFFICE 2,1illb8lll RHEOSTAT Original application May 26,1933, Serial No.

672,955. Divided and this application October 7, 1935, Serial No. 43,978

3 Claims.

My invention relates to electrical control devices and more particularlyto a rheostat of the general type used for volume control and relatedpurposes in radio circuits, and this application 5 is a division of myco-pending application Serial No. 672,955, filed May 26,1933 which hasmatured into Patent 2,043,777.

It is an object of my invention to employ a spring arm of very lightmaterial, which ongages the contact shoe of the resistance element.

A further object of my invention is to embody an inconspicuous,serviceable device whereby a violent jolt of the unit will not dislodgethe contact shoe from the pressure arm.

A further object of my invention is to construct the terminal members sothat an inadvertent bending or displacement of the low resistanceterminalmember will cause no change in the low resistance hop-off.

Still another object is the provision in such devices of terminals orconnection lugs adapted to slotted or notched engagement with a basemember, and having foot portions for engagement with a resistor member.

Other objects of this invention are to provide an improved device of thecharacter described, that is easily and economically produced, which issturdy in construction and which has a maximum of eificiency andaccuracy.

With the above and related objects in view, my invention consists in thefollowing details of construction and combination of parts, as will bemore fully understood from the following specification, taken inconjunction with the drawings, in which:

Figure 1 shows a fragmentary sectional view of my invention embodied ina rheostat and combined with a snap switch;

Figure 2 is a plan view of the resistance ele- 4 ment and terminals;

Figure 3 is a perspective view of the contactor arm, its support andshaft;

Figure 4 is a rear view of the contactor arm support, showing theunsymmetrical placing of the holding rivets;

Figure 5 is a fragmentary side elevational view showing the swedging outof the shaft holding means at the end of the bushing;

Figure 6 is a sectional view taken on the line 66 of Figure 5; a

Figure 7 is a plan view of the we into the insulating plate;

Figure 8 is a fragmentary side elevational view of Figure 7, moreclearly showing the burr on the edge of the slots of the washer;

sher biting Figure 9 is a fragmentary side elevational view showing theattachment of a terminal;

Figure 10 is a fragmentary plan view of the terminal;

Figure 11 is a plan view of a modified contactor arm and contactingshoe;

Figure 12 is a front view of the shoe and conta-ctor arm shown in Figure11;

Figure 13 is a fragmentary sectional view of a tandem arranged rheostatembodying my invention;

Figure 14 is a plan view of another type of pressure arm wherein thearms are supported in a manner to prevent twisting;

Figure 15 is a modification of the arm as disclosed in Figure 14;

Figure 16 is a plan view of a tandem arranged pressure arm;

Figure 17 is the opposite face of Figure 16;

Figure 18 is a cross-sectional View taken on the line l8-i8 of Figure14.

Figure 19 is a cross-sectional view taken on the line lib-l9 of Figure15;

Figure 20 is a plan view of the rheostat shown in Fig. 1;

Figure 21 is a plan view of my rheostat, showing a cover grounding plateand positioning lugs; and

Figure 22 is a broken sectional view of the rheostat shown in Figure 1.

Referring now to the drawings in more detail, particularly to Figs. 1, 2and 3, it will be seen that the instrumentalities of the rheostat aremounted upon a base or mounting disc Ill which may conveniently beformed of an insulating material such as phenol condensation productcommonly known as bakelite. The resistance element 02, preferably acarbonaceous coated strip of generally arcuate shape, is placed upon oneof the fiat faces of the base or mounting disc l0, and is heldthereagainst by terminal members M and i6 engaging its ends.

As will be seen in Figs. 2, 9 and 10, the terminal member it, of asingle strip of conducting material of uniform thickness, has a foot 58disposed in engagement with one end of the resistance element l2 and ispierced for the reception of an attaching means, shown for convenienceas an eyelet 2D. The foot portion iii of the terminal contains anarcuate recess 22 so that the length of the terminal edge in closeproximity to the shoe, when the shoe is adjacent the terminal, will begreater than if the terminal had a straight edge extending across theresistance element, and as a consequence the minimum resistance betweenthe shoe and the terminal is lower than would I otherwise be obtained.

The terminal member l4, at the low resistance end of the resistanceelement, may have a diverg necessary will be to make the high resistanceterminal complementary to the low resistance terminal, that is, one ofthe members is a right hand member and the other a left hand member.

The diverging extension 24 also functions to keep a low initialresistance in the circuit until the switch, mounted on the cover, isclosed.

The neck 88 of the terminal I8 is bent sharply adjacent the foot portionI8 and is fitted in a slot 82 in the periphery of the mounting plate IIIto prevent the terminal member from being turned circumferentially withrespect to this plate. The neck is then turned back upon itself andtapers in width, as indicated at 84. The terminal extends at an angle tothe plane of the cylindrical casing face to permit the easy attachmentof the various lead wires. To prevent the displacement of the footportion of the terminals l4 and l8 with a consequent increase in theminimum resistance, should there be an axial bending of the terminals,narrow sections l and I! respectively have, been provided in the lugportion of the terminals so that bending will first take place at thesepoints and no harm result.

Bushin Mounted concentrically in the disc II is a suitable iournalbushing or thimble, generally designated as A, which may also serve as apanel mounting device for the unit. This bushing A may be threadedexteriorly as at 88 for the reception of a nut by which the assembly isclamped upon a suitable panel or bracket, that is, by the usual and wellknown type of mounting, and the bushing also has a central longitudinalopening 88 therethrough.

The bushing A contains an annular flange 48 disposed against the surfaceof the disc l0 upon I which the resistance element i2 is located, and ifdesired, this flange 48 may be serrated on one face as shown at 42 sothat it will bite into the disc II and lock that disc against rotationwith respect to the bushing.

A shoulder or swaged portion 48, of smaller diameter than the flange andemerging from the flange, protrudes through the base opening 44 and alsothrougha'central opening in a holding clamp B, and the end of theshoulder 48 is swelled to grip the face of the clamp and to engage aplurality of spaced niches 48 (Fig. 20) in the clamp B for theprevention of rotary motion of the disc and the holding clamp B in adirection about the axis of the shaft, and in a, direction along theshaft. If further rotational restraint is desired, burrs are providedalong the radial edges of the niches 48, so that they engage the disc l0when the shoulder 48 of bushing A is swaged in place. This verydefinitely locks the disc l8 and clamp B together and may be usedinstead of the knurling 42 on the flange 48. Protruding lugs 88 on theclamp B are adapted to co-operate with holes in the panel, upon whichthe rheostat is to be mounted, and prevent rotation of the rheostatrelative to the panel.

Contactor arm An operating shaft, generally designated C, and journaledin the thimble A, is comprised of a cylindrical portion 48 of suitablelength and a reduced substantially rectangular end 58, see Figs. 3 and4. A thin insulating plate D of substantially circular formation, has aplurality of extending cars 52 and 54 on the periphery adapt ed toengage a suitable stop member 58 protruding from the stud H4 forlimiting the rotation of the arm in either direction, and the plate,also, has a central elongated opening 58 to fit onto the end 50 of theshaft; The insulating plate is placed upon the reduced end 58 of theshaft 48 and a washer, generally designated E, having a central openingto also fit onto the reduced end 58 of the shaft is placed thereon andthe face of the reduced end is then swaged over, holding the shaft C,the plate D and the washer E in position. The washer has, see Figs. 7and 8, a plurality of radial slots or notches 88 and 82 with burrs Si,83, 84 and 85 along the radial edges of the notches, which burrs areadapted to bite into the insulating plate, thus preventing relativerotation of the shaft and insulating plate.

A resilient contactor or pressure arm F, preferably of a single piece ofsuitable thin conducting material and supported by the plate D, iscomprised of an arcuate shaped cantilever arm 88 supported ateach end byintegral formed yoke portions 88 and 18, which yoke portions in turn areunited to a central slip-ring section 12 having an internal diametersubstantially larger than the diameter of the shaft 48, as shown inFigure 3, to space the slip ring section from the shaft in an insulatingrelationship thereto. The contactor armis also provided with aperipheral cut-out portion 14, which is adapted to fit about aneccentrically mounted operating pin 18 carried by the insulating plateD. The arcuate shaped arm has verging from its unsupported mid-portion aprojecting tip or boss 18 adapted to engage the perforated disc or shoe28, which engages the resistance element. However, the tip may beconstructed to actually engage the resistance element, or may take avariety of forms as shown in Figs. 11 and 12, as hereinafter more fullydescribed.

A modified pressure arm G, Figs. 11 and 12, has a short conical boss 80and two projecting lugs 82 and 84.

A fiat contact shoe 85 has two diametrical opposed holes 88 and 88therein, which receive the projecting lugs 82 and 84, respectively, ofthe pressure arm. The pressure exerted by the arm G is directed againstthe central portion of the 1 shoe 85 by the conical boss 88 engaging theupper surface of the contact shoe.

The contact shoe is drawn along the resistance element by one or theother lug of the pressure arm engaging the edge of one of the holes inthe shoe 8!, so that the shoe is always pulled along the resistanceelement.

The contactor or pressure arm F is mounted upon the insulating plate bymeans of suitable eyelets or rivets 98 and 82, see Figs. 3, 16 and 17,which eyelets or rivets are unsymmetrlcally placed, as will behereinafter further described. The arm F is so mounted that the tip 18will be approximately equi-spaced from the extending ears '2 and 54,Fig. 17.

Now referring again to my preferred embodiment shown in Fig. 3, thestamped-out arm F has an aperture 94 near the rivet 92 to provideclearance around a rivet or bolt 9| (Fig. 17), when a second arm H (Fig.16) is inserted on the opposite face for a tandem arranged series ofrheostats.

Pressed out projections 96 and 98 to each side of the free end of thecantilever arm and extending in a direction opposite to that 'of the tipI8 are adapted to engage one'face of the insulating disc to. prevent thecontacting shoe from separating from the lug "I8.

Considerable difficulty is experienced when manufacturing rheostats, insecuring a uniform predetermined pressure between the contacting shoeand the resistance element, and between the spring member K and thecontact arm F, both of which are very necessary if low resistancecontacts and long life are to be expected. Predetermined pressures areobtained with my rheo= stat by assembling the parts in proper axialalignment and then applying the desired pressure to the shaft C in anaxial direction and in such a manner that it is resisted by the pressurebe tween the contacting shoe and resistance element plus the pressurebetween the arm F and spring member K. These pressures are maintained byswaging the shaft, when in the desired position (Figs. 1, 5, and 6), atI0 I, so that it is enlarged at this point and forms a shoulder thatbears against the washer I00, which is in contact with one end of thethimble A.

-It is particularly to be noted that with this method of assembly, nounnecessary strain whatsoever is placed upon the contactor or resilientarm by pressing the contact shoe 28 in engagement with the resistanceelement during the swaging action.

Slip-ring and washer Disposed upon the surface I02 of the thimble A isan insulating washer J Figs. 1 and 2, having diametrically placedperipheral notches IM and I06 therein.

A ring-shaped slip-ring member, generally des ignated K, and having aconcave face H08 adjacent the insulating washer J, has a short lug H0and a long lug II2, Figs. 1, 2 and 13, extending from the periphery ofthe face I08. The lugs H0 and H2, when suitably bent, extend or fit intothe notches I04 and I06 of the insulating washer, and the long lug isalso adapted to provide the electrical take-off for the derivedelectrical circuit. The stud I I4 serves to connect the long lug II2 ofthe slip-ring member to a terminal I I 6 and secures rthe slip-ring andterminal in electrical relationship. It is to be particularly noted, seeFig. 1, that the slip-ring K is aaially resilient to provide a goodelectrical contact with the movable slip-ring I2.

Both the washer J and the slip-ring member K are provided with centralaligned openings for receiving the control or operating shaft C, theapertures formed in the slip-ring member K being of a larger diameterthan the opening or aperture through the washer J, so the slipringmember K will be spaced from the control shaft and thus insulatedtherefrom.

Tandem Heretofore, the tandem or double type of rheo stat construction,in which the pressure arms were insulated from each other (shown in Fig.

13) required a. large casing, but by my novel un-= symmetricallyarranged contact arm F supported upon the insulating base 10 (shown inFigs. 16 and 17) by eyelets 90 and $2, I econoniize in space by placingan additional contact arm l-I, similar in structure to the arm E,(butone arm beingLso-called right-handed" and the other left-handed)upon the vacant face. N8 of the insulating strip and securing it inplace with eyelets di and 93. It will be noted that there is noelectrical connection between the two arms, as each arm is cut out bothto clear the eyelets that hold the arm in place, and to clear the shaft.I have thus provided an insulated pressure arm for the second rheostatsection without the addition or" another shaft, bushing, or mountingplate, such as has been used in the past. The second rheostat section iscomprised of a second insulating base i120, held in the housing M0 bythe eyelet Ni, and positioned angularly by formed-in sections in thehousing cooperating with notches in the periphery of the base I20. Aresistance element 143 is carried by the base M20 and is contacted by ashoe I44 driven by the pressure arm H. Terminals for the resistanceelement and for the spring connector K, which contacts the arm H, areprovided and extend through notches in the base M0 and through anopening in the metal housing I40 that is sulficiently large to providegood insulation.

Snatch. operation in order to provide for the operation of a switch orcircuit controller, the insulating disc D may be provided with aneccentrically mount: ed pin it.

This pin l6 projects normal to the plane of the insulating disc and islocated to engage an operating arm or ear it? of the switch mechanism S.A movement of the insulating disc 10 will,

therefore, operate the switch mechanism. The switch S, shown by way ofexample, may be any preferred type of switch suitable for this purpose,such as the switch shown in my co-pending application, Serial No.602,006, filed March 30, 1932, to which application reference is nowmade for the details of the construction of the switch and the manner ofmechanical arrangement.

Mounting The casing ill, within which the rheostat is housed, isprovided with a plurality of projecting ears U50, which are registeredin peripheral slots tilt, [126, 025i and Mill on the base and bent overto attach the casing to the plate. Theregistration of the ears withtheir respective slots (12d, 8%, 620 and H30, accurately aligns andholds the housing with respect to the plate both in a rotary directionabout the axis of the shaft and in a direction along the shaft. By thismeans, the alignment of the rheostat and switch may be predetermined sothat the two will function cooperatively.

The casing or housing for the rheostat, which also supports the switch,may be attached to the base by any suitable means, but preferably by themeans as disclosed in either of my co-pend ing applications, Serial No.668,757, filed May 1, 1933 or Serial No. 6713031, filed May 15,193$,which has matured into Patent No. 2,059,813.

It is in many cases advmtageous to provide a rheostatv enclosed'airnostentirely in metal, so that all of the operating parts areelectrostatically shielded from outside electrical disturbances. This isespecially true when a switch is mounted on the cover and is to be usedfor switching a fluctuating current. I have found it possible to veryefllciently and economically accomplish both of the above results withthe plate L (Figs. 21 and 22) from which the lugs 239 are formed.

Plate L is mounted over the base l so that the insulating base is almostcompletely shielded. This plate L is also in electrical contact with themounting bushing or thimble A, which will normally be mounted on agrounded metal panel, and has clinched over onto it the ears I50 of thecover member II. It is therefore necessary to ground only the thimble toaccomplish the necessary electrostatic shielding of the rheostat fromthe switch and other external disturbances. In many instances, it ispossible to effect economies in the manufacture of radio sets byextend-- ing the grounding plate to one of the terminals of theresistance element. i

In Fig. 21, I have shown plate L carrying a terminal ll, which replacesone of the regular terminals. This terminal is normally connected toground by virtue of being a part of the plate L, which is normallygrounded. It is also con-- nected to one end of the resistance element(the end that is desired to be grounded) by the eyelet 2M and a washeror plate on the inside of the rheostat bearing against the element andheld in place by the eyelet. When a grounded terminal is not desired,the plate L is made according to the dotted lines 210.

Two ears 238 integral with the plate L and formed at right angles to itare adapted to register with holes in the mounting panel to preventrotation of the control relative to the panel during assembly andafterward. A washer or spacer 216 is assembled on the thimble A,preferably in a permanent manner, to provide an even substantialmounting surface and to space the terminals and ears away from thepanel.

Referring now to Figs. 14 and 18, I show a pressure arm of the samegeneral type as, but having certain valuable improvements over, the armcovered in my Patent No. 1,913,686 of June 13, 1933. With the arm of myprior patent, there was a tendency for the two converging sections totwist when a pressure was applied against the contact paddle, due to thebowing of the yoke section caused by the pressure on the ends of theyoke being in a reverse direction to that on the contact projection.This twisting seriously impaired the flexibility of the arm "as a whole,since the legs were free to bend in the desired direction for only asmall part of their total length, the balance of their length beingtwisted and not free to bend.

This is overcome in the arm disclosed in Figs. 14 and 18 bystrengthening the yoke carrying the lug 2I2 by a rib or offset portion2H), and by strengthening the rear section with a rib or offset portion2. By strengthening the front and rear yoke portions in this manner,twisting of sections 204 and 208 is prevented, and a gooddistribution offlexing obtained.

I have accomplished this same end in the arm shown in Figs. 15 and 19 bysecuring the ends of portions 250 and 252 to the plate 254, which isquite rigid, by eyelets 258 and by strengthening the front yoke portionby bending a portion 262 at a substantial angle to the main part of theyoke 258.

Although the invention has been described in considerable detail, suchdescription is intended as illustrative rather than limiting, as theinvention may be variously embodied, and the scope of the invention isto be determined as claimed.

I claim as my invention:

1. In a variable resistance device, the combination with a flatinsulating base having a notch in-its peripheral portion, a resistanceelement on said base, and a contact shoe engaging said resistanceelement, of a terminal comprising a foot portion overlying and engagingsaid resistance element, an integral connection lug portion, and

a reversely bent offset portion extending downwardly to seat in thenotch in said base to assist in maintaining the terminal in fixedposition upon the base, said reversely bent portion having an outerportion extending outwardly away from the center of the base betweensaid foot portion and said connection lug portion to form a solderreceiving recess.

2. In a variable resistance device, the combination with a flatinsulating base having an open slot in the edge thereof, and aresistance element on one face of said base, .of a terminal having afoot portion lying against said face of said base in contact with theend of said resistance element, a connection lug portion extending awayfrom said base and a reversely bent portion forming a solder trappingrecess intermediate said foot portion and said connection lug and seatedin said slot to assist in maintaining the terminal in fixed positionrelativeto said insulating base.

3. In a variable resistance device, the combination with a flatinsulating base having portions cut away in its peripheral region, aresistance element on said base, and a contact member engaging saidresistance element, of a terminal comprising a foot portion overlyingand engaging said resistance element, an integral body portion extendingoutwardly and upwardly away from the center of the base and having areversely bent oflset part seatable in the said cut-away portions ofsaid base to assist in maintaining the terminal in fixed relation tosaid base and forming an open solder trapping recess connecting saidfoot and said body parts.

' NEWTON c. SCHELLENGER.

